Gelled slurry explosive composition containing a terpolymer gelling agent



United States Patent US. Cl. 149-41 13 Claims ABSTRACT OF THE DISCLOSURE An improvement in gelled slurry explosive compositions which comprises employing as a gelling agent a terpolymer consisting of an acrylamide, an acrylonitrile and an acrylic acid, said gelling agent being crosslinked if desired with an inorganic polyvalent metal salt.

BACKGROUND OF INVENTION There have been many attempts to provide gelled explosive compositions which have long-term storage, -water resistance, -stability, -strength and -fluidity characteristics. Gelled explosive compositions, usually contain (a) ammonium nitrate alone or in conjunction with a metal nitrate, such as, for example, sodium nitrate, (b) a sensitizer, (c) water and usually contain as an addi tional constituent a gelling or thickening agent to provide some of the previously indicated desirable characteristics. Various gelling and thickening agents have been employed heretofore, such as, for example, natural occurring gums such as guar and karaya, and synthetic gelling agents such as, for example, polyacrylamides, described in US. Patent No. 3,097,120 issued July 9, 1963 to Bowkley et al. These have not proved to be completely successful. Although these various gelling and thickening agents have provided some of the characteristics desired in gelled explosive compositions, the gels have still been plagued with disadvantages such as variations of the gums from one batch to another, deterioration of crosslinked gelling agents upon standing, over crosslinking with time, insufficient gel strength to withstand cracking and the eroding action of ground water and low resistance to extrusion through cracks in boreholes. Attempts, heretofore, to remedy these serious defects have produced slurries which resist water extrusion but which are too stilf to be readily pumpable at normal operating pressures. Less viscous slurries are hampered by erosion and leaching difiiculties.

These previously encountered disadvantages have now been overcome, by modifying previously known slurry and gelled type explosive compositions by incorporating a novel terpolymer as the gelling agent. The gelling agent is crosslinked in the presence of the other constituents of the explosive composition and provides gelled explosives which have long-term storage life, good water resistance, stability, strength and good pumpability characteristics. Furthermore the degree of crosslinking can be closely controlled; the resulting crosslinked gel is stable over a wide range of pH values and remains stable over wide fluctuations in temperatures.

SUMMARY OF THE INVENTION The present invention comprises improved gelled explosive compositions employing a terpolymer consisting of an acrylonitrile, an acrylamide, and an acrylic acid, as the gelling agent. All percentages hereinafter designated are percent by weight unless otherwise specified.

As employed herein, the terms acrylamide desig- 3,446,681 Patented May 27, 1969 acrylic acid designates acrylic acid and/or methacrylic acid.

PREFERRED EMBODIMENTS In practice, the novel gelled explosives comprise a gelling agent which in turn comprises a terpolymer consisting of (a) from about 1 to about 60 percent of an acrylonitrile, (b) from about 25 to about 98 percent of an acrylamide, and (c) from about 1 to 15 percent of an acrylic acid. Preferably the terpolymer consists of (a) about 30 percent of an acrylonitrile, (b) about 68 percent of an acrylamide, and (c) about 2 percent of an acrylic acid, and other constituents commonly employed in said explosive compositions.

The acrylonitrile provides a copolymer which is insoluble in water, but still soluble in aqueous ammonium nitrate solutions. An acrylic acid, in an amount of about 2 percent by weight of the terpolymer provides carboxyl crosslinking sites of the desired amount to crosslink tightly and yet prevent syneresis of liquid upon standing. It is preferred that the acrylonitrile content be maintained at a maximum of about 30 percent by weight of the terpolymer. The water insolubility of the polymer is lowered at lower concentrations and the terpolymer gel slurry becomes more fragile instead of rubbery at concentrations greater than about 30 percent.

In practice, the present novel gelled explosives usually are prepared by admixing the terpolymer gelling agent with the other constituents of the explosive gel in a like manner as with previously employed gelling agents. The terpolymer is usually provided in an amount of from about 0.1 to about 5.0 percent by weight of the explosive composition and preferably 0.5 to 2.5 percent. Usually, about 1 percent by weight of the terpolymer provides an explosive composition with the most favorable characterisics, and therefore is preferred. At concentrations greater than about '1 percent the explosive gel is very rubbery and holds its shape for prolonged periods of time. The terpolymer is usually dissolved in a salt solution and introduced into the explosive composition and crosslinked.

The gelled explosive composition may contain in addition to the terpolymer a suspending agent such as, for example, natural gums, e.g., guar gum, wheat flour, cereal products and the like. The suspending agent can be employed to provide an explosive composition of uniform consistency, the constituents of which will not separate upon long standing in the uncrosslinked condition. The amount of such constituent will depend upon the terpolymer molecular weight and about 0.25 percent by weight of a suspending agent is usually suflicient to provide the necessary settling stability of the components of the explosive composition. Usually the slurries are crosslinked within a few hours after preparation and therefore a suspending agent is unnecessary.

Polyvalent inorganic metal salts are used as crosslinking agents for the terpolymer. For low molecular weight terpolymers, chromic, ferric, ferrous and zirconyl cations are preferred. Zirconyl and ferric salts are less preferable in higher molecular weight terpolymers since they cannot be readily dispersed in the explosive composition due to the rapid rate of crosslinking of the terpolymer and thus prevent a low distribution of the constituents of the slurry. Chromic salts are unique as crosslinking agents since they evidence a time delayed crosslinking characteristic. Therefore, it is possible to add the chromium salt to a slurried explosive composition containing the terpolymer just prior to pumping it into a borehole. The explosive composition will remain fluid for a sufiicient period of time to allow normal pumping pressures to be used, while crosslinking the terpolymer within a sufficient period of time to provide a highly water resistant gelled explosive composition in the borehole. Iron shows similar delayed crosslinking characteristics but only at acrylic acid concentrations which are usually too low to provide adequate gelling properties by the terpolymer. Each of the crosslinking agents has a different temperature range for the most useful results. For example, aluminum and iron can be used at very low temperatures (20-30 F.) whereas chromium usually must be employed at higher temperatures since at low temperatures the crosslinking time is usually unduly long.

The concentration of the crosslinking agent has little effect on the induction time (i.e., the time for the viscosity of the explosive gel to start rising rapidly) and the degree of crosslinking once a minimum amount of crosslinker is added. In actual practice about 0.1 gram of crosslinking agent per 100 grams of explosive composition is used to provide a maximum degree of crosslinking of the terpolymer. The amount of crosslinking agent required will usually vary with the particular agent employed; for example, usually about 0.16 gram of chromium nitrate, Cr (NO .9H O, per 100 grams of explosive slurry is used to achieve maximum crosslinking of the terpolymer, at a one percent by weight concentration.

The pH of the explosive composition effects the induction time of the terpolymer. A pH within the range of from about 3.5 to about 7.0 is preferred, for the most rapid crosslinking of the terpolymer with Cr+ ion as the crosslinking agent. Other pH ranges can be defined for other crosslinking agents.

As indicated previously, iron can cause a crosslinking of the terpolymer. Therefore, when an immediate crosslinking of the terpolymer is not desired, e.g., during shipment of the explosive composition, iron as an impurity may have to be prevented from contaminating the compositions. Various methods may be employed for assuring iron-free systems such as, for example, utilizing iron-free constituents in the explosive mix and preventing contact with containers made of corrodible steel. Also, certain agents may be employed which complex with iron thus preventing free iron ions from crosslinking the system. Monosodium hydrogen phosphate, sodium citrate, sodium ethylenediamine tetraacetic acid and sodium sulfide have proven to be effective in preventing premature crosslinking by free iron ions in the explosive composition. However, if a system is to be crosslinked immediately, small amounts of iron actually may be desirable.

The novel terpolymer can be employed as the gelling agent in the well-known slurry explosive compositions which usually contain as essential components, (a) an inorganic oxidizing salt, (b) a sensitizer and/ or fuel and (c) water.

Examples of inorganic oxidizing salts include, for example, ammonium, alkali metal and alkaline earth metal nitrates, perchlorates and chlorates. Specific examples of commonly employed salts are ammonium nitrate, ammonium perchlorate, sodium nitrate, sodium perchlorate, potassium nitrate, potassium perchlorate, magnesium nitrate, magnesium perchlorate, calcium nitrate, other like salts and mixtures thereof. Usually the explosive composition contains from about percent to about 90 percent by weight of the inorganic salts. Preferably at least one of the inorganic oxidizing salts is ammonium nitrate.

Examples of suitable sensitizers include high explosives such as TNT, smokeless powder, PETN, RDX, pentolite, other organic nitrates, nitro compounds and nitrated high explosives; metallic sensitizers such as, for example, particutate light metals, metalloids, particulate aluminum, magnesium, silicon, iron, ferrosilicon, ferrophosphorus, magnesium-aluminum alloys, aluminum-silicon alloys, alloys of aluminum containing at least 20 percent aluminum, alloys of magnesium containing at least 20 percent magnesium, ASTM designated alloys such as ZKlO, ZK60, HK31, A231 and other like alloys, boron, vanadium, chromium, thorium, titanium, tungsten, and

mixtures and alloys of these metals, and the like; carbonaceous materials, such as, finely divided carbon, corn starch, sugar, and petrolic liquids such as crude oil and liquid hydrocarbons derived therefrom, formamide, glycols, urea, alcohols and the like. Carbonaceous materials are usually employed in an amount up to about 20 percent by weight of the explosive compositions. Metallic sensitizers usually range in size from about 4 mesh to about 200 mesh and are employed in amounts up to about 60 or more percent by weight of the explosive composition. Various combinations of sensitizers can also be employed such as, for example, metallic fuels and fuel oils are commonly used together and high explosives such as, forexample, smokeless powder and metallic fuels are employed in the same explosive composition.

Other ingredients can also be employed in the slurry composition such as solvents for said inorganic oxidizing salts and/or liquid fuels and sensitizers such as petrolic liquids including, for example, crude oil and liquid hydrocarbons derived or fractioned therefrom and kerosene, diesel fuel, petroleum distillate, and unrefined petroleum components, water, liquid organic fluid extenders such as monohydroxy alkanols, ethylene glycol, propylene glycol, glycerol, formamide, dimethyl sulfoxide, methanol, mix tures of these various constituents and other like materials. The amount of petrolic liquid and/ or fluid extender usually ranges up to about 10 percent by weight of the explosive. Suitable solvents include ammonia, ammonical solutions, e.g., Divers fluid, water and the like.

An example of a specific slurry explosive composition which may be improved by including the novel terpolymer of the present invention is disclosed in US. Patent No. 3,307,986, issued Mar. 7, 1967. A slurry explosive composition is disclosed in the patent consisting of ammonium nitrate from 0 to about 85 percent; alkali metal nitrate to about percent; particulate aluminum from about 5 to about 20 percent; water from about 5 to 20 percent, and a gelling agent from about 0.2 to about 2.5 percent. A preferred gelled explosive composition in disclosed consisting of sodium nitrate from about 5 to about 40 percent; ammonium nitrate from about 10 to about percent; particulate aluminum from about 10 to about 30 percent; water from about 6 to about 16 percent; liquid water-miscible liquid extenders from about 2 to about 16 percent; and a water swellable, hydrophobic, crosslinkable gum and crosslinking agent from about 0.5 to about 1.5 percent.

The particulate aluminum employed in the explosive composition usually ranges from about 4 to about 150' mesh US. Standard Sieve and has a gauge (thickness) of from about 0.25 to about 30 mils. The metal is further characterized in having a particle size distribution wherein from about 60 to about 80 percent of the aluminum is from about 12 to 50 mesh the balance being substantially 50 to mesh and wherein from about 5 to 10% of the particles have a gauge of up to 1 mil, from about 70 to about 80% have a gauge of up to 1 mil, from about 70 to about 80% have a gauge of from 1 to about 10 mils and the balance are substantially from 10 to about 30 mils in gauge.

Ordinarily, the aluminum metal employed has a particle size andv gauge distribution as set forth in Table I.

TABLE I Metal particle size Distribution, (US. Standard Sieve), mesh: percent 30-50 60-70 50-100 25-35 100-150 About 5 Metal gauge, mils: Distribution, percent Up to 1 6-8 Preferably the metal ranges from about 0.025 to about mils in gauge.

Aluminum as employed in the patent is meant to include both aluminum and aluminum alloys containing at least about 60% by weight aluminum.

Liquid organic fluid extenders which are disclosed in the patent are those having a favorable carbon-oxygen ratio such that there is substantially no detrimental competition of the carbon with the metal for available oxygen in the system. Monohydroxy alkanols containing from 1 to about 4 carbon atoms, ethylene and diethylene glycol, propylene glycol, glycerol, formamide and mixtures thereof are particularly suitable. Preferably methanol, ethylene glycol, glycerol and formamide are used as extenders or diluents in the explosive composition. Ordinarily, formamide, which has a low carbon content and relatively high boiling point it utilized as the liquid extender. Certain polyglycols tend to destroy the water resistance of the terpolymer and therefore should normally be avoided.

Ordinarily, from about 5 to about 40 percent and preferably from about 12 to about 35 percent of the total weight of ammonium nitrate is present as a solid, particulate grained material passing a 20 mesh US. Standard Sieve. While ammonium nitrate is usually present as the oxidizer, at least a part of the ammonium nitrate may be replacedby sodium-, lithium-, potassiumor other alkali metal nitrates if desired, to obtain increased or decreased density, sensitivity or other properties.

The properties of the explosive composition defined in the indicated patent can be improved by employing the previously defined terpolymer as the gelling agent in the composition. The terpolymer can be provided in an amount of from about .1 percent to about 5.0 percent by weight of the explosive, preferably from about 0.5 to 2.5 percent by weight, the exact amount depending on the desired properties of the gelled composition. Higher concentrations of the terpolymer produce a stitfer gel with less flowability but greater resistance to erosion by a water stream. The terpolymer is usually employed in an amount equal to about 1 percent by weight of the explosive composition. At this concentration, the crosslinked terpolymer provides a gelled explosive composition having sufiicient strength to withstand erosive effects. As previously indicated herein, it is sometimes desirable to employ a suspending agent, such as, for example, guar gum, in an amount equal to about 0.25 percent of the explosive composition.

Other slurry explosive compositions well known in the art can be improved by employing the novel terpolymer as defined hereinbefore as a gelling agent in said composition. The gelled slurry compositions can be prepared by admixing an aqueous inorganic salt solution containing a desired quantity of the terpolymers dissolved therein, with the other solid and liquid constituents of a specific explosive composition. The terpolymer is then crosslinked, employing a suitable crosslinking agent to provide a gelled slurry explosive composition having superior gelled characteristics. The terpolymer can be prepared by standard polymerization methods employing the monomeric units of the terpolymer.

The following examples are included to facilitate a complete understanding of the present invention but it is understood that they do not limit the invention to the specific embodirnens incorporated therein.

Example 1 Percent Constituents: by weight Guartec UFD gum 0.25 Propylene glycol Terpolymer solution, terpolymer (1.0), water 6 (4.0), ammonium nitrate in solution (5.0) 10.0

NaNO (crushed) 10.00 Additional water 6.00 Formamide (iron free) 10.00 Aluminum (particulate) 10.00 NH4NO3 The terpolymer consisted of approximately 68 percent acrylonitrile, 30 percent acrylamide and 2 percent acrylic acid.

The explosive composition was prepared as follows:

1) A commercially available Guartec UFD gum and propylene glycol were mixed in a mixer and kept agitated to produce a pourable mix.

(2) Formamide and water were mixed in a mixer and maintained at a temperature of from about 70-75 F.

(3) The Guartec-glycol mix from step 1 was added to the formamide-water mix with constant agitation for about 20 minutes. A clear uniform gel was formed.

(4) A terpolymer solution consisting of an aqueous ammonium nitrate solution containing the dissolved terpolymer was added with agitation to the mixer containing the clear gel as formed in step 3.

(5 Particulate NaNO NH NO and aluminum were then added to the composition mix of step 4 and thoroughly mixed.

The terpolymer was crosslinked tion which was about one molar with respect to the Cr(NO About 0.9 ml. of crosslinking solution per one pound of explosive mix was employed. The resulting explosive composition was in a gel form which was highly resistant to leaching and erosion effects of water. A portion of the explosive was detonated and showed good results.

with a Cr(NO solu- Example 2 A comparison of explosive compositions containing various gelling agents was made in order to determine the segregation rate of each gelling agent. A basic eX- plosive composition having the following formulation was employed as the test medium, parts by weight:

Aluminum 10 Crushed NaNO prills 1O Formamide 10 Water 10 NH NO crushed prills 59 To gram samples of this formulation was added various gelling agents including the addition of a terpolymer, consisting of about 68 percent acrylonitrite, 30 percent acrylamide and 2 percent acrylic acid with 0.25 percent of Guartec UFD gum. The settling time, i.e., time for a noticeable layering of the constituents was recorded and the times are set forth in the following Table II for 1 part by weight concentrations of each gelling agent.

The terpolymer in combination with a recognized suspending agent such as Guartec UFD, a commercially available guar gum, kept the constituents in suspension for at least 1 day. The crosslinked terpolymer also provided an improvement in the other important characteristics including excellent anti-leaching and erosion properties, resistance to thermal decrosslinking and syneresis, over other gels. Furthermore the terpolymer system showed superior properties over the polyacrylamide gelling agent as to long term stability, resistance to syneresis and the like.

Various modifications may be made in the present invention without departing from the spirit or scope thereof for it is understood that we are limited only as defined in the appended claims.

We claim:

1. A gelled slurry explosive composition comprising: an inorganic oxidizing salt, a sensitizer, water, a gelling agent consisting of a terpolymer consisting of, as percent by weight of the terpolymer;

(a) from about 1 to about 60 trile,

(b) from about 25 to about 98 percent of an acrylamide,

(c) about 1 to about 15 percent of an acrylic acid,

and a cross-linking agent for said terpolymer.

2. The gelled slurry explosive composition as defined in claim 1 wherein the said explosive composition ineludes in addition to said terpolymer, a suspending agent in the amount of about 0.25 percent by weight of the said explosive composition.

3. The gelled slurry explosive composition as defined in claim 1 wherein said terpolymer comprises from about 0.1 to 5.0 percent by weight of the slurry explosive composition.

4. The gelled slurry explosive composition as defined in claim 1 wherein the terpolymer consists of on a percent by weight of the terpolymer:

(a) about 30 percent acrylonitrile,

(b) about 68 percent acrylamide, and

() about 2 percent acrylic acid.

5. The slurry explosive composition as defined in claim 4 wherein said terpolymer comprises from about 0.5 to 2.5 percent by weight of the explosive composition.

6. The gelled slurry explosive composition as defined in claim 1 wherein said crosslinking agent comprises a polyvalent metal salt.

7. The gelled slurry explosive composition as defined in claim 6 wherein said crosslinking agent comprises a chromic salt.

8. The jelled slurry explosive composition as defined in claim 1 which comprises on a percent weight basis:

(a) to about 60 percent alkali metal nitrate,

(b) from about 10 to about 85 percent ammonium nitrate,

(c) about to about 25 percent water,

(d) from about 5 to about 40 percent particulate aluminum, said aluminum ranging in size from about 4 to about 150 mesh U.S. Standard Sieve and having a gauge of from about 0.025 to about 30 mils and being further characterized in having a particle size distribution wherein from about 60 to about 80 percent is from about 12 to about 50 mesh the balance being substantially 50 to 100 mesh and wherein from about 5 to about percent of the particles have a maximum gauge of about 1 mil, from about 10 to about 80 percent have a gauge of from 1 to about 10 mils, balance ranging from 10 to about 30 mils in gauge, and

percent of an acryloni- (e) a gelling agent, consisting of a terpolymer which consists of, as percent by weight of the terpolymer: about 30 percent acrylonitrile; about 68 percent of acrylamide, and about 2 percent of acrylic acid, said terpolymer comprising from about 0.1 to 5.0 percent by weight of said explosive composition, and

(i) an inorganic polyvalent metal salt crosslinking agent. I

9. The gelled slurry explosive composition as defined in claim 8 wherein said terpolymer comprises from about 0.5 to about 2.5 percent by weight of said explosive composition.

10. The gelled slurry explosive composition as defined in claim 8 wherein said inorganic polyvalent metal'salt crosslinking agent comprises a chromic salt.

11. The gelled explosive composition as defined :in claim 8 wherein in addition to said terpolymer a suspending agent is employed in the amount of about 0.25 per cent by weight of the gelled explosive composition.

12. The gelled slurry explosive composition as defined in claim 8 which comprises: j (a) from about 5 to about 40 percent sodium nitrate,

(b) from about 15 to about percent ammonium n'itrate,

(c) from about 6 to about 16 percent water,

(d) from about 2 to about 16 percent of a ganic water-miscible liquid extender,

(e) from about 10 to about 30 percent particulate aluminum, said aluminum having(1) apatricle size of from about 30 to about mesh wherein the particle size distribution ranges from about 60 to about 7 percent of about 30 to 50 mesh, from about 25 to about 35 percent of from about 50 to 100 mesh, balance from about 100 to about mesh and (2) a gauge of from about 1 to about 15 mils and distribution such that about 6 to about 9 percent of the particles have a maximum thickness of about 1 mil, from about 14 to about 17 percent range from about 1 to about 15 mils, from about 73 to about 77 percent range from about 5 to about 10 mils, balance susbtantially from 10 to about 15 mils.

13. The gelled slurry explosive composition as defined in claim 1 wherein said explosive composition includes a particulate metal fuel.

liquid, or-

References Cited UNITED STATES PATENTS 3,097,120 7/1963 Hoffman et a1. l4949 3,097,121 7/1963 Bowkley et al 149-60 3,321,344 5/1967 Arbie 149-56 3,341,383 9/1967 Bergwerk 149- 60 3,355,336 11/1967 Lyerly 14960 BENJAMIN R. PADGETT, Primary Examiner.

S. I. LECHERT, Assistant Examiner.

US. (21. X.R.

zgz gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,zw,5,5a Dated m 27 1969 Inventor(s) Thomas E. Slykhouse, Kenneth E. Werth and Henry Volk It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

{ Column 6, line 49, for "acrylonitrite" read acrylemide "'1 column 8, line 32, for "7" read 7O SIGNED AND SEALED NW 4 19m Anew Edmdm'mmm mam-1m E. 501mm, .m. Au i ()ffiw Oomissioner or Patents 

